Gerd Pühlhofer, Landessternwarte Heidelberg + IAAT Tübingen
Pulsar wind nebulae: The VHE – X-ray connection
HESS = High Energy Stereoscopic System
Photo: © Philippe Plailly H.E.S.S.:H.E.S.S.: HighHigh EnergyEnergy StereoscopicStereoscopic SystemSystem H.E.S.S. collaboration:
MPI für Kernphysik, Heidelberg Humboldt Univ. Berlin Ruhr-Univ. Bochum Univ. Hamburg Landessternwarte Heidelberg LLR, Ecole Polytechnique, Palaiseau LPNHE, Univ. de Paris VI-VII PCC, College de France, Paris Observatoire Paris-Meudon, LUTH CEA Saclay Univ. de Grenoble Univ. Monpellier II CESR Toulouse Durham Univ. University of Leeds Dublin Inst. for Adv. Studies Nicolaus Kopernikus Astr. Center, Warsaw Jagiellonian University, Cracow Institute of Nuclear Physics, Warsaw Four twelve meter optical dishes Space research center, Warsaw Charles Univ., Prag Khomas Highlands (Namibia) Yerewan Physics Inst. North-West Univ., Potchefstroom 1800 above sea level Univ. of Namibia, Windhoek Start of full operation end of 2003 Univ. Tübingen H.E.S.S. event reconstruction parameters: • Primary direction: < 0.1° • Field of view: 3° FWHM • Shower core: 10m → Energy resolution: 15% • Energy range: 0.1–100 TeV
Cherenkov light from shower particles
Photo: © Philippe Plailly THE VHE (>100 GeV) Galactic plane from the HESS GP survey THE VHE (>100 GeV) Galactic plane from the HESS GP survey Let’s blank out:
• SNR shells: RXJ 1713-3946, Vela Jr, RCW 86 • Binaries: LS 5039, PSR B1259-63 • Stellar cluster association: HESS J1023-575 (Westerlund 2) • Molecular cloud associations (confirmed and likely): Galactic ridge, HESS J1745-303, HESS J1800-240 (W28 A), HESS J1834-087 (W41)
• For several of the remaining sources, a pulsar wind nebula (PWN) identification is certain • For the vast majority of the rest, a PWN scenario is at least possible OverviewOverview
• Some general statements about the relation between X-ray and VHE pulsar wind nebulae
• Young vs. middle-aged and relic PWN
• Pevatrons and INTEGRAL
• Identification problem of large-offset VHE PWN
• Underluminous X-ray PWN and associated issues
Warning: totally biased towards VHE-detected PWN GeometryGeometry ofof aa pulsarpulsar windwind (nebula)(nebula)
Sketch by Slane
Neutron star Cold, non-emitting flow Acceleration of particles at termination shock Visible (i.e. emitting) pulsar wind nebula Possibly interaction with surrounding SNR (e.g. reverse shock) XX--rayray emittingemitting PWN:PWN: samplesample studystudy
Chandra PWN review, Kargaltsev & Pavlov, astro-ph/0801.2602 XX--rayray emittingemitting PWN:PWN: samplesample studystudy
ε or η: Efficiency of current pulsar energy loss into given observation band
Large scatter of X-ray synchrotron efficiencies
But fairly good correlation between nonthermal magnetospheric and PWN emission
Chandra PWN review, Kargaltsev & Pavlov, astro-ph/0801.2602 “Usual”“Usual” XX--rayray PWNPWN seenseen withwith ChandraChandra
Tori Bow shocks and wakes ''Mouse'' Gaensler et al. 2004
Tori and bow shocks/tails reflect pulsar geometry resp. motion This is not what will be dealt with in this talk
Gaensler et al., 2006
IC 443 Ng & Romani 2003 PWN:PWN: thethe largestlargest identifiedidentified GalacticGalactic VHEVHE populationpopulation
Several firmly HESS HESS identified VHE pulsar wind Nebulae (PWN)
Many VHE PWN candidates
Why identified: • known pulsar • morphology HESS HESS matches with X- ray PWN
Most VHE PWN are •extended • displaced from the pulsar CosmicCosmic microwavemicrowave backgroundbackground ……
… serves as homogeneous target for Inverse compton scattering of electrons
WMAP Ka Credit: WMAP Science Team CMBCMB ++ GalacticGalactic “foreground”“foreground”
In addition, stellar and dust radiation fields can boost IC emission
Credit: WMAP Science Team WMAP Ka (Thermal and nonthermal) Stellar and dust photon fields are hard to access (esp. 3-D) TheThe youngyoung CrabCrab NebulaNebula (1000(1000 years)years)
HEGRA collaboration, ApJ 2004, 614, 897
(Northern Hemisphere source)
synchrotron branch IC branch
compact source, high B-field (160 µG) → • high synchrotron efficiency, IC emission comparatively low • synchrotron photons produce relevant target field for IC (“SSC”) → IC coupled to B-field again TheThe youngyoung CrabCrab NebulaNebula (1000(1000 years)years)
HEGRA collaboration, ApJ 2004, 614, 897 MeV
TeV
IC branch TheThe youngyoung CrabCrab NebulaNebula (1000(1000 years)years)
HEGRA collaboration, ApJ 2004, 614, 897 MeV
+IC from stellar fields
TeV
IC branch
Extended pulsar wind nebulae from middle-aged pulsars • are simpler because IC scattering off external, in principle well known target photon fields • are much more common… FFX // FFVHE ……
… or FVHE / FX: a widely used diagnostic tool useful for investigating VHE – X-ray source associations
from Kargaltsev et al., ApJ 670, 2007 LifetimeLifetime ofof VHEVHE--emittingemitting electronselectrons
from Aharonian et al., A&A 460, 2006 τ ≈ × 5 -3 -1 -1 VHE 3.1 10 (wr/eV cm ) (E/1 TeV) years
η -3 2 wr = wph + 0.025 eV cm (B/µG) η normalisation factor due to KN suppression
Wph energy density in photon fields (CMB, IR, starlight)
→ For low B-fields, the lifetime of VHE-emitting electrons can greatly exceed the lifetime of the X-ray - synchrotron emitting (higher-energy) electrons → The VHE PWN reflects the injection evolution of the pulsar HESSHESS J1640J1640--465:465: aa “relic”“relic” PWNPWN scenarioscenario
MOST
XMM-Newton
Funk, Hinton, GP, et al., ApJ 662, 2007 G21.5G21.5--0.9,0.9, KesKes 75:75: CrabCrab companions?companions?
G21.5-0.9 Edot = 3.3 × 1037 erg s-1 Kes 75 Chandra Chandra t ~ 1000 years (« tc) Camilo et al., ApJ 637, 2006
Edot = 8 × 1036 erg s-1 ≈ t ~ 800 years ( tc) Magnetar-like behaviour
Gotthelf et al., ApJ 542, 2000 Credit: NASA/CXC/GSFC Credit: NASA/CXC/Manithoba/ Gavriil et al. Matheson & Safi-Harb Ng et al., astro-ph/0804.3384
HESS coll., Djannati-Atai et al. astro-ph/0710.2247
FX / FVHE ~ 30 → B ~ 15µG
FX / FVHE ~ 10 → B ~ 10µG HESS: unresolved HESS: unresolved Below equipartition B-fields Vela-X: a middle-aged PWN Vela-X: a middle-aged PWN 1 ’
ROSAT contours: extended X-ray synchrotron(?) nebula Chandra: compact X-ray nebula
VHE spectrum (peak!) interpreted as IC scattering 1 → × 45 ° Enonth ~ 2 10 erg
Caveat: → this isn‘t the entire PWN (as seen in radio) Color map: H.E.S.S.: → sensitivity limited? VHE IC nebula VHEVHE ++ XX--raysrays inin casecase ofof aa hadronichadronic sourcesource
Energy X-rays TeV flux electron synchrotron ~B² electron IC ~ ph.-field E2 dn/dE proton:π0
IC high B field (>10 µG) ~ B-2
Photon energy VelaVela X:X: nucleonicnucleonic PWN?PWN? Vela Jr. (HESS)
Vela X (HESS)
Hadronic model Horns et al, A&A 451, 2006 Leptonic model, e.g. de Jager et al., astro-ph/0803.0116
• Debate still somewhat open • Some criticism on the hadronic scenario • In this talk, the standard view of leptonically-dominated PWN is adopted • (hadronically mediated acceleration) “Relic”“Relic” pulsarpulsar windwind nebulaenebulae
HESS J1825-137: Identification with X-ray PWN G 18.0-0.7
XMM-Newton Gaensler et al., ApJ 2003
Aharonian et al. (HESS coll.) A&A 460, 2006 ArchetypeArchetype forfor aa TeVTeV –– XX--rayray PWNPWN associationassociation
HESS J1825-137: Identification (mainly) by TeV spectral imaging
> 2.5 TeV Aharonian et al. (HESS coll.) 1 – 1.52.5 TeV A&A 460, 2006 < 1 TeV AsymmetricAsymmetric VHEVHE PulsarPulsar WindWind NebulaeNebulae
''Crushed Plerions'' Offset VHE PWN Pulsar
X-ray PWN
VHE PWN Blondin et al., 2001
Or pulsar proper motion/ + IC electron lifetime larger than synchrotron lifetime + larger particle injection efficiency in the past ram pressure? ConfirmationConfirmation ofof thethe crushedcrushed PWNPWN scenarioscenario ……
… in the HESS J1825-137 / G 18.0-0.7 system
Pavlov et al., ApJ 675, 2008
pulsar proper motion (VLA) perpendicular to relic PWN direction HESSHESS J1813J1813--178:178: IdentificationIdentification withwith XX--rayray PWN?PWN?
2.5’
XMM-Newton
Funk et al., A&A 470, 2007
If INTEGRAL source can be identified with X-ray (synchrotron) nebula → Object is a “Pevatron” HESSHESS J1813J1813--178:178: „„PevatronPevatron““ hypothesishypothesis
Chandra:
z Compact source: identified as pulsar
z PWN dominates up to ~10 keV → INTEGRAL association Helfand et al., ApJ 665, 2007 with PWN not unplausible HESSHESS J1813J1813--178:178: IdentificationIdentification withwith XX--rayray PWN?PWN?
INTEGRAL pulsars with known Edot
Dean & Hill (astro-ph/0804.3420, RN):
→ Extreme pulsar properties
z Either underluminous in INTEGRAL band (ε=0.01)
z Or spin-down age decoupled from SNR age (cf. e.g. G11.2-0.3) HESSHESS J1809J1809--193:193: twotwo PSRPSR counterpartscounterparts
Dean et al., MNRAS 384, 2008 + Chandra reanalysis INTEGRAL of G11.2-0.3
HESS J1809-193 (roughly)
50% of the 20-100 keV flux from PSR J1811- 1925 is from the PWN But no evidence for a morphological INTEGRAL 18-60 keV connection to the VHE source TheThe PWNPWN aroundaround PSRPSR J1809J1809--19171917
Chandra
Chandra preliminary Kargaltsev & Pavlov, ApJ 670, 2007 HESS coll., Komin et al., astro-ph/0709.2432 HESS → The PWN around PSR J1809- 1917 is very likely contributing to HESS J1809-193 → Especially in this case, multiple components in the VHE source cannot be excluded preliminary VHEVHE PWNPWN candidatescandidates
HESS coll., A&A 472, 2007 z Classification because of association with powerful pulsar z no X-ray PWN required for this classification z Large ε-values are in principle possible (decoupling from Edot)
HESS coll., A&A 472, 2007
HESS collaboration, preliminary A&A, 2007
H.E.S.S. source of the month May 2007 HESS coll., Gallant et al., AIP 978, 2008 HESSHESS J1718J1718--385:385: aa VHEVHE PWNPWN candidatecandidate
XMM, 0.5-10 keV XMM, point sources subtracted
Yellow contours: HESS
Hinton et al., A&A 476, 2007 compact but still extended X-ray emission around PSR J1718-3825 → likely the compact X-ray PWN, but no clear link to the HESS source + Suzaku pointing to search for weak diffuse emission HESSHESS J1718J1718--385:385: aa VHEVHE PWNPWN candidatecandidate
Suzaku, 0.5-7 keV XMM, point sources subtracted
GP et al. 2007 (Suzaku conf.): diffuse emission could morphologically connect XMM PWN with HESS source HESSHESS J1718J1718--385:385: aa VHEVHE PWNPWN candidatecandidate
A (or C)
B
adopted from Hinton et al., A&A 476, 2007 ““UnderluminousUnderluminous”” PWNPWN
PSR J1838-0655 (X-ray pulsar discovered using XTE) Gotthelf & Halpern, astro-ph/0803.1361
Detection of PWN around PSR J1617- 505 with Chandra, but association with HESS J1616-508 inconclusive Chandra PWN review, Kargaltsev & Pavlov, astro-ph/0801.2602 Kargaltsev et al., astro-ph/0805.1041 HESSHESS J1837J1837--069:069: ChandraChandra ++ RXTERXTE
White contours: Map: Chandra ACIS 2-8 keV VLA 90 cm
PSR J1838-0655
Gotthelf & Halpern, astro-ph/0803.1361
- Edot = 5.5×1036 erg s-1 η -3 - PWN,X = 10 - age = 23 kyr → Good counterpart to Yellow contours: HESS HESS source → But some interesting / open issues AXAX J1838.0J1838.0--0655:0655: CompactCompact sourcesource dominatesdominates
INTEGRAL source (Malizia et al. 2006, Lutovinov et al. 2005): Possible hard X-ray – VHE connection
→ INTEGRAL source is presumably not the ASCA ≡ extended PWN Compact source (pulsar) (cf. HESS J1813-178) ReflexionReflexion halohalo aroundaround AXAX J1838.0J1838.0--0655?0655?
Predehl & Schmitt 1995 (ROSAT) AX J1838.0-0655:
N ~ 5 ×1022 cm-2 →τH sca (1keV) = 2.5 !!!
Open circles: additional intrinsic absorption
Cf. G21.5-0.9, Bocchino et al. 2005 SummarySummary
• VHE astronomy provides a new window to PWN physics • Efficient way to detect (relic) PWN because of the ubiquitous target photon fields for IC (CMB, + dust and starlight), independent of B-field • Combination of X-ray and VHE allows e.g. determination of B-field (with caveats) • Currently, for identification of VHE PWN mostly morphological arguments and efficiency into VHE flux is used • X-rays reflect mostly current spin-down power (short synchrotron lifetime), whereas VHE, similar to radio, should allow to access the entire deposited pulsar energy budget (for moderately low B-fields)
• Cf., e.g., to RPWN / Rshock – “radius method” by Swaluw & Wu (ApJ 555, 2001) based on radio-PWN to infer the initial spin rates AtAt thethe sensitivitysensitivity limitlimit ofof currentcurrent VHEVHE instrumentsinstruments
H.E.S.S. (adaptively smoothed) Two shell-type supernova remnants Plausible hadronic emission scenarios exist for both sources
HESS collaboration, astro-ph/0803.0682 & astro-ph/0803.0702
HESS source of the month April 2008 AtAt thethe sensitivitysensitivity limitlimit ofof currentcurrent VHEVHE instrumentsinstruments
Chandra H.E.S.S. (adaptively smoothed)
→ Nonthermal X-ray sources hinting at pulsars / PWN
HESS source of the month April 2008
HESS collaboration, astro-ph/0803.0682 & astro-ph/0803.0702 CTA:CTA: TheThe CherenkovCherenkov TelescopeTelescope ArrayArray CTACTA ((CherenkovCherenkov TelescopeTelescope Array):Array): targettarget sensitivitysensitivity
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